Conventionally, in an image processing device, an input image is generally reduced at a prescribed ratio to create a reduced image. The reduced image is created by smoothing the input image while extracting pixels at prescribed sampling intervals.
However, when the image has periodicity which is inconsistent with the sampling intervals, moire occurs. The occurrence of moire is particularly significant at a dot portion such as Screen-tone. This is because the number of dots included in an area to be smoothed changes with periods dependent to the sampling intervals and the image periods, and a pixel value after smoothing also varies with periodicity, for each sample point.
In order to eliminate such moire occurring at the dot portion, a method is provided for detecting dots in advance and smoothing the dot portion across an area of a certain size. However, there are many different types of image periods of dots, and a relatively large area must be smoothed in order to eliminate occurrence of the moire at dot portions of all types, resulting in deterioration of image quality.
Moreover, random dots that have no periodicity may also be subjected to a similar smoothing process, which is unnecessary, causing further deterioration of the image quality.